1. Field of the Invention
The present invention relates to a load driving apparatus which is configured to drive a load to be switched on and off, and to a method for controlling the load driving apparatus.
2. Description of the Related Art
In the recent years, a load driving apparatus which is configured to drive a load such as a Light Emitting Diode (LED), a laser diode, etc. is required to drive the load at a high speed, as information grows in capacity and is processed at a high speed. In particular, in the field of optical communication, a digital optical communication is widely used wherein a light emitting element such as the LED and laser diode as the load is pulse-driven. As the amount of communication processed by the optical communication is increased, there is a demand for a load driving apparatus capable of ON/OFF driving of the light emission at a high speed.
Conventionally, there is disclosed a technique for applying a predetermined bias voltage to a light emitting element, to such an extent that does not cause the light emitting element to emit light, also during an OFF period during which the light emitting element is switched off, as the method for switching the light emitting element ON at a high speed, namely as the method for switching the light emitting element form the OFF state to the ON state in a short period of time.
Japanese Patent Application Laid-open No. 2001-326569 which corresponds to U.S. Patent Application Publication No. US2001/0043093A describes that the problem to be solved thereby is “to minimize the increase in electric current consumption, to reduce a transient responding time, to accelerate modulation and to obtain output light of small pulse waveform distortion even in the LED of a large internal capacity”; and as the solution to the problem, Japanese Patent Application Laid-open No. 2001-326569 describes that “an LED is an element in which the current begins to flow rapidly when a voltage pulse Vd applied to an intrinsic diode of an electric equivalent model reaches a value very close to a peak value, and which is capable of providing optical output proportional to the electric current flowing forward. By utilizing this property of LED, a rectangular voltage pulse having large current driving ability by low output impedance is supplied to a directly connected LED load. Alternatively, a voltage pulse having two high levels such with a high level boosting voltage just after starting and with a voltage returning from the high boosted voltage to a prescribed voltage a predetermined period of time later is supplied to a directly connected LED load. The low level of this voltage pulse is DC-biased in the range of voltage capable of maintaining the extinction ratio of an LED output signal required for the request of a system”.